1. Technical Field
The present invention relates to a driving method of an electrophoresis display device, an electrophoresis display device, and an electronic apparatus.
2. Related Art
An electrophoresis display device displays an image by migrating electrophoresis particles by creating a potential difference between a pixel electrode and a common electrode which are disposed to face one another and have an electrophoresis element between them. JP-A-2002-116733 discloses an electrophoresis device having a memory function by which an image is maintained even while the potential difference is not caused between the pixel electrode and the common electrode.
However, if a predetermined time passes after the image is displayed on the electrophoresis display device, the electrophoresis particles gathered at the electrodes scatter. As a result, reflectance of the image displayed with white is decreased and reflectance of the image displayed with black is increased. Therefore, there is a problem in that contrast is lowered. In order to improve the lowered contrast, JP-A-3-213827 discloses a driving method in which a refresh operation is repeatedly performed at every 10 seconds to 10 minutes after the image writing operation is performed.
The refresh operation is to improve the contrast which is lowered after 10 or more minutes after the image displaying is performed. However, the inventors of this invention have found a phenomenon called kick back in which contrast is lowered just several seconds after the image writing is performed besides the above-mentioned contrast lowering.
FIG. 20 is a timing chart showing an image writing operation in a known electrophoresis display device. In FIG. 20, potentials applied to a segment electrode 1035W of a segment performing a white display, a segment electrode 1035B of a segment performing a black display, and a common electrode 1037 are shown. FIG. 20 also shows an image writing period for displaying an image and an image maintaining period for maintaining the displayed image. The structure of an electrophoresis display device driven by a segment driving method is shown in FIGS. 1, 2, and 4. The segment electrodes 1035W and 1035B in FIG. 20 correspond to two segment electrodes 35 of adjacent segments 40 shown in FIG. 2 and the common electrode 1037 corresponds to a common electrode 37.
FIG. 21 shows measurement result of changes in reflectance of the known electrophoresis display device. In FIG. 21, a reference numeral 1001 denotes reflectance of a white display and a reference numeral 1002 denotes reflectance of a black display.
During the image writing period, a high potential is applied to the segment electrode 1035B and a low potential is applied to the segment electrode 1035W. The common electrode 1037 is applied with a pulse in which high potentials and low potentials alternate. In FIG. 21, the image writing period begins from 0.5 seconds and continues for 0.5 seconds. Thus, the reflectance of a white display is increased and the reflectance of a black display is decreased.
When the image writing period terminates, the image maintaining period begins. During the image maintaining period, the segment electrode 1035B, 1035W, and the common electrode 1037 are in a high impedance state.
However, right after the image writing period terminates, the reflectance of a white display is remarkably decreased and the reflectance of a black display is moderately increased. That is, it can be known that the contrast lowering occurs right after the image maintaining period begins. This problematic phenomenon is the kick back phenomenon discovered by the inventors.
The inventors clarifies that the lowering range of the contrast attributable to the kick back depends on moisture content of the electrophoresis display element by experiments.